The present invention relates generally to a suction pipe for use in a liquid transfer system and, more particularly, to an adjustable suction pipe incorporating an improved pressure activated seal to prevent air from being drawn into the pump inlet and adversely effecting pump performance.
A suction pipe is typically used in a liquid transfer system to convey the liquid from the supply tank to a pump inlet for dispensing the liquid inside the supply tank. To accommodate various depths of supply tanks, a suction pipe is typically comprised of various sections and can be made adjustable with a sliding joint between at least two section members. Typically, a suction pipe would include a bottom or first section, a middle or second section, and an extension or third section. A seal is typically located between the bottom section and the middle section to prevent air from being drawn into the pipe and thereafter into the pump inlet which is attached to the suction pipe exterior of the supply tank. If the fluid level within the supply tank is above the seal joint, the joint has no impact on pump performance. However, if the fluid level in the supply tank is below the seal joint, the joint must incorporate a seal sufficient to prevent air from being drawn into the suction pipe and then into the pump inlet which can adversely affect pump performance. If an extension section is utilized, the extension section is typically threaded onto one end portion of the middle section in such a manner that a seal between the members forming this connection juncture is not necessary. Since the middle section is adjustable and collapsible within the bottom pipe section, an appropriate seal between the joinder of these two suction pipe sections is necessary to prevent air and/or fluid from inadvertently entering the suction pipe and adversely effecting pump performance.
FIGS. 1 and 2 illustrate examples of prior art seal devices associated with adjustable suction pipes known in the industry. The seal 10 is made up of multiple components including an O-ring 12, a rubber U-cap member 14, and a body member 16. The seal is energized with the O-ring 12 and the overall seal 10 is fabricated using a spin-weld operation. This operation includes spinning adjacent components relative to each other at a rotation speed sufficient to frictionally fuse the relative components together. While the seal 10 is effective, the multiple component design and use of a spin-weld operation increases the manufacturing cost and complexity of the seal and joinder of the seal to the suction pipe.
The seal 20 illustrated in FIG. 2 discloses another known plastic seal which includes seal edges 22. While seal 20 is relatively simple and easy to install, as the pump inlet pressure decreases, the seal edges 22 tend to pull away from the interior surface of the suction pipe thereby allowing air to be drawn into the suction pipe through the joint established between suction pipe members 24 and 26 starting at the joinder point indicated by arrow 28. Air is drawn into suction pipe member 25 because once the pump is activated, as will be hereinafter further explained, the pressure inside the suction pipe will be lower than atmospheric pressure and if the joint/seal arrangement 20 is above the fluid level within the supply tank, atmospheric pressure air can be sucked into pipe member 24 as previously explained. This can cause cavitation in the pump and will adversely affect pump performance.
Although the known suction pipe seals are effective under most operating conditions, there is a need for an improved seal arrangement which will more positively avoid atmospheric air from being drawn into the suction pipe when the fluid level within the supply tank is below the location of the seal thereby avoiding adverse pump performance as well as cavitation, and thereby improving the overall performance of the suction pipe and the pump. As a result, the present invention is directed to overcoming one or more of the problems set forth above and represents an improvement over the known prior art seal arrangements associated with adjustable suction pipes.